1. Field of the Invention
Embodiments of the present invention generally relate to a plasma processing chamber configured to process semiconductor substrates. Particularly, embodiments of the present invention relate to a plasma chamber having an electrode with a nonplanar top surface.
2. Description of the Related Art
When processing substrates in a plasma environment, the uniformity of the plasma intensity will affect the uniformity of processing. For example, during a plasma enhanced chemical vapor deposition (PECVD) process to depositing advanced patterning film (APF), such as amorphous carbon, the within-substrate thickness is mainly determined by the plasma intensity uniformity. More material is deposited on the substrate where the plasma intensity is high and less material is deposited on the substrate where the plasma intensity is low. Similarly, in an etching process, more material is likely to be removed or etched from the substrate corresponding to a high plasma intensity area.
Therefore, non-uniformity in plasma processes can significantly decrease device performance and lead to waste because the deposited layer or etched portion is not consistent across the substrate due to the non-uniformity in plasma intensity.
Excellent process uniformity has become increasingly important as semiconductor devices become continuously more complex. Uniformity is important in both the feature-scale (<1 micron) and the wafer-scale (300 mm). Non-uniformities arise from a variety of reasons, for example variation of concentration of different ingredients of a processing gas, such as etching and passivating species, ion bombardment flux and energy, and temperature within the feature profile and across the wafer.
One of the non-uniformities observed is the edge effect in a PECVD chamber. The edge effect refers to a stronger plasma in an area which is about 15 millimeter away from the edge of the substrate. The edge effect may be observed at a hump region near the edge of the substrate after an APF deposition.
FIG. 1A schematically illustrates a conventional plasma reactor 100 susceptible to an edge effect. The plasma reactor 100 comprises an upper electrode 101 disposed over a substrate support 102. The substrate support 102 is configured to support a substrate 105 thereon so that the substrate 105 faces the upper electrode 101 during processing. The upper electrode 101 may be a showerhead configured to evenly distributing a processing gas to a process volume between the substrate support 102 and the upper electrode 101. A lower electrode 103 is disposed below the substrate 105, usually embedded in the substrate support 102. A RF power source 104 may be applied between the upper electrode 101 and the lower electrode 103 to generate a capacitive induced plasma between the upper electrode 101 and the substrate support 102.
The plasma intensity in the plasma reactor 100 generally relates to the concentration of the processing gas and density of an electric field 106 between the upper electrode 101 and the lower electrode 103. The size difference between the upper electrode 101 and the lower electrode 103 and sharp corners may cause an increase the electric field 106 near an edge region, thus, increased plasma intensity near the edge.
FIG. 1B schematically illustrates a partial sectional view of the substrate 105 with a film 107 deposited thereon. As a result from the edge effect, a hump 108 is observed near the edge of the substrate 105.
Other non-uniformities also exist during plasma processing due to chamber structure and/or operating parameters.
Therefore, there is a need for apparatus and method for processing a semiconductor substrate with increased uniformity.